1. Field of the Invention
The present invention relates generally to voltage detectors and, more particularly, to a voltage detector circuit with a programmable threshold point.
2. Related Art
Battery-powered portable electronic devices, such as laptop computers and cell phones, require circuits to detect power-on and low power conditions of their battery power supplies. Without such circuits, the portable electronic devices may operate improperly or fail.
Circuits that detect power-on conditions are commercially available in the form of power supply monitoring chips. These chips typically have power supply voltage following circuits that track the power supply voltage and output a signal during turn-on when the power supply voltage surpasses a pre-determined threshold point on the rising-edge of the power supply voltage. The threshold point signifies a voltage sufficient for device operation and serves to provide safe startup of the devices by indicating when the power supplies have stabilized at acceptable voltage levels.
Circuits that detect low power conditions are also commercially available in the form of microprocessor reset chips. These chips track the power supply voltage and output a signal when the power supply voltage drops below a threshold point. In this case, the threshold point signifies that the power supply voltage has fallen to a level which is insufficient for device operation or that the power supply voltage is decreasing toward a critically low level.
One problem with previously developed technologies is that there are no chips having circuits that detect both the power-on and low power conditions. While it is possible to incorporate both a power monitoring circuit and a microprocessor reset circuit on a single chip, doing so would require a substantial amount of surface area for the chip. Additionally, connecting the two circuits unduly increases the complexity of the chip.
Another problem with previously developed technologies is that the individual power monitoring circuit chips and microprocessor reset circuit chips themselves are too large to fit inside small portable electronic devices, which are becoming smaller and smaller. One reason for this is that both types of chips require a circuit that generates a reference voltage from which a threshold point value is derived. This reference voltage generation circuit is relatively large and thus increases the size of the individual chips.
Another problem with previously developed technologies is that commercial reset chips only provide a small number of programmable threshold point values (e.g., 2 or 3). Chips offering a large number of threshold point values have preset levels for the threshold point values and are only available as discrete components.
It is also important that the amount of power or current consumed by circuits or chips in battery-powered portable electronic devices is low. This ensures that the battery-powered portable electronic devices can operate for commercially acceptable periods of time.
Accordingly, what is needed is a circuit that can be implemented on a single chip, that is capable of detecting both power-on and low power conditions, that can be programmed to detect a large number of threshold points values, and that consumes a low amount of current.